1. Field of the Invention
This invention relates to the bonding, cutting and printing of polymeric materials.
2. Background of the Invention
Sheets of polymeric materials, including films, e.g., polyethylene films, and nonwoven fabrics, e.g., spunbonded and meltblown polypropylene nonwoven webs, which materials typically are thermoplastic, have been used to make a variety of commercial products, such as diapers, feminine care products, gloves, and the like. Assembly of these products generally involves the steps of: (1) cutting specified shapes from the sheets; (2) bonding two or more sheets together along specified contours; and (3) in some cases, printing a pattern on portions of the sheets which form the outer surface of the finished product. The bonding, cutting, and printing steps can, in general, be performed in any order, e.g., pre-cut and pre-printed sheets can be bonded together or full sheets (webs) can be bonded together, printed, and then cut.
Various techniques have been used to perform the cutting, bonding, and printing operations. For example, cutting dies having prescribed contours corresponding to those of the finished article have been used to cut polymeric sheets. Bonding has been performed by applying glue to the sheets in specified patterns, as well as through the use of heated mandrels having shapes which correspond to the areas in which bonding is to occur. Bonding also can be accomplished by application of ultrasonic energy. See Flood, Gary, N. "Ultrasonic Bonding: A Practical View," Advanced Forming/Bonding Conference, Insight 86 International Conferences, Washington, D.C., Sep. 7-9, 1986, Section VII, pages 1-13. Printing has been performed using classical printing techniques, such as lithography.
A fundamental problem with the existing techniques is the extensive, and thus expensive, set-up steps which are required for each product which is to be manufactured. Thus, cutting dies, gluing jigs, and the like have to be specifically fabricated on a product-by-product basis. In most cases, the cost of this tooling can only be supported by relatively large production runs. Also, in terms of manufacturing logistics, if a single production line is to produce multiple products, the tooling for each product must be stored between uses and the line must be shut down for an extended period of time each time the product being manufactured is to be changed. As with the tooling itself, these manufacturing problems add to the final cost of the product.
The use of radiant heat as part of the manufacturing process for nonwoven fabrics has been disclosed in U.S. Pat. No. 3,420,724. Specifically, this patent describes preparing a web of synthetic fibers having intermittent dark and light colored areas and applying radiant heat to the web to melt the fibers in the dark areas and thus bond the fibers together to form the finished fabric. The dark areas are distributed throughout the fabric and between 5 and 50% of the fabric's fibers lie in dark areas.
Additionally, U.S. Pat. No. 3,189,702 to Wall et al. relates to the making and sealing of packages. Briefly, a continuous narrow uniform cusped smooth-edged stripe pattern of strongly radiation-absorptive thermally non-adherent ink is imprinted on a surface of a first film segment. A second film segment is placed over and in pressure-contact with the imprinted surface at least along and adjacent said stripe. The stripe then is irradiated through one of the film segments at an intensity and for a time adequate to produce at said stripe a heating effect sufficient to cause the occurrence of autogenous bonding between the film segments only along narrow fusion bands contiguous to the edges of the strip and of a width permitting longitudinal separation of the film segments along the line by hand pulling without tearing of the segments. At least one of the film segments is transmissive of the radiation.
U. S. Pat. No. 4,504,529 to Sorensen et al. discloses a xerographic method for dry sensitization and electroless coating of an insulating surface and a powder for use with the method. The toning powder contains a sensitizing Sn.sup.+2 compound. The toning powder can contain an infrared-absorbing material which aids in the adherence of the powder to the substrate. The three examples present in the reference describe the preparation of three different powders, all of which are to be fixed or adhered to the substrate by a solvent-based method.
U.S. Pat. No. 4,025,378 to Amsden et al. relates to a method for attaching a polyethylene sleeve label to a polyethylene bottle. The label has heat-absorbing areas which, when subjected to a heat source, cause the label and bottle to fuse together in such areas, thereby bonding the label to the bottle. Only smooth-surfaced substrates are involved and the label itself apparently undergoes localized melting to cause attachment to the bottle.
U.S. Pat. No. 4,156,626 to Souder relates to a method and apparatus for selectively heating discrete areas of surfaces with radiant energy. The method involves the use of focused radiant energy to heat in discrete areas a thermoplastic adhesive. The degree of heat absorption can be varied by the use of variations in the shading or darkness of a coating of printed materials. However, the energy source must provide a high degree of radiation of wavelengths in the visible range. In addition, the energy source is focused in order to vary the size of the surface area so as to vary the area heated and/or to vary the intensity of heating of the area.
U.S. Pat. No. 3,909,582 to Bowen relates to a method of forming a line of weakness in at least one but not all layers of a multilayer laminate. The method comprises effecting relative movement between a beam of radiant energy of a particular predetermined wavelength and intensity and the laminate so that the energy is selectively relatively absorbed by the at least one layer in an amount and manner that alters the structure of the layer and thereby forms a line of weakness in the laminate. The beam of radiant energy is supplied by a laser and is intended to affect fewer than all of the layers in the laminate. The absorptive materials of this reference apparently require the formation of vapors or a gas upon exposure to the radiation.